U.S. patent application number 12/875391 was filed with the patent office on 2011-03-03 for apparatus, system, and method for access procedure enhancements.
This patent application is currently assigned to VIA TELECOM, INC.. Invention is credited to Jian Gu, Anthony Lee, Guotong Wang, Shu Wang.
Application Number | 20110051697 12/875391 |
Document ID | / |
Family ID | 43454968 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110051697 |
Kind Code |
A1 |
Wang; Guotong ; et
al. |
March 3, 2011 |
Apparatus, System, and Method for Access Procedure Enhancements
Abstract
A mobile communication device for access procedure enhancement
is provided. In the mobile communication device, a wireless module
performs wireless transmissions and receptions to and from a
service network. Also, a controller module transmits an access
probe to the service network via the wireless module, and
retransmits the access probe in response to not receiving an
acknowledgement of the access probe from the service network via
the wireless module in a waiting period of time. The waiting period
of time is determined according to a coherence-time related offset.
The controller module further repeats the retransmission of the
access probe until the acknowledgement of the access probe is
received from the service network via the wireless module
Inventors: |
Wang; Guotong; (Beijing,
CN) ; Gu; Jian; (Beijing, CN) ; Lee;
Anthony; (San Diego, CA) ; Wang; Shu; (San
Diego, CA) |
Assignee: |
VIA TELECOM, INC.
San Diego
CA
|
Family ID: |
43454968 |
Appl. No.: |
12/875391 |
Filed: |
September 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61239763 |
Sep 3, 2009 |
|
|
|
61241003 |
Sep 9, 2009 |
|
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Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H04W 28/0236 20130101;
H04W 52/146 20130101; H04W 52/221 20130101; H04W 52/48 20130101;
H04W 74/004 20130101; H04W 52/325 20130101; H04W 28/06 20130101;
H04W 52/54 20130101; H04W 74/085 20130101; H04W 52/367 20130101;
H04W 52/343 20130101; H04W 52/36 20130101; H04W 52/228 20130101;
H04W 72/0486 20130101; H04W 52/04 20130101; H04W 76/10 20180201;
H04W 48/10 20130101; H04W 52/50 20130101; H04L 5/0055 20130101;
H04W 52/362 20130101 |
Class at
Publication: |
370/336 |
International
Class: |
H04J 3/00 20060101
H04J003/00 |
Claims
1. A mobile communication device for access procedure enhancement,
comprising: a wireless module performing wireless transmissions and
receptions to and from a service network; and a controller module
transmitting an access probe to the service network via the
wireless module, retransmitting the access probe in response to not
receiving an acknowledgement of the access probe from the service
network via the wireless module in a waiting period of time, and
repeating the retransmission of the access probe until the
acknowledgement of the access probe is received from the service
network via the wireless module, wherein the waiting period of time
is determined according to a coherence-time related offset.
2. The mobile communication device of claim 1, wherein the access
probe is first transmitted using a transmission power which is
determined according to reverse-link load information of the
service network.
3. The mobile communication device of claim 1, wherein the access
probe is first transmitted using a transmission power and
retransmitted according to one of the following: using the same
transmission power in a predetermined number of repeats within a
probe sequence, and the controller module further increases the
transmission power for the retransmissions of the access probe
after the predetermined number of repeats within the probe
sequence; using the same transmission power within the probe
sequence, and the controller module further increases the
transmission power for the retransmissions of the access probe
within a next probe sequence; and using the transmission power with
an incremental manner for the retransmission of the access probe in
each repeat within the probe sequence.
4. The mobile communication device of claim 1, wherein the service
network broadcasts reverse-link load information, and the
controller module further determines a cell in the service network
to which the access probe is transmitted according to the
reverse-link load information.
5. The mobile communication device of claim 1, wherein the access
probe comprises information concerning a length of message data,
and the controller module further transmits another access probe
with the message data to the service network via the wireless
module in response to receiving a pre-acknowledgement of the access
probe from the service network via the wireless module.
6. The mobile communication device of claim 5, wherein the access
probe and the another access probe are transmitted and
retransmitted respectively according to the following: the access
probe is first transmitted using a transmission power within a
probe sequence, and the controller module further increases the
transmission power for the retransmission of the access probe in
each repeat within the probe sequence until the pre-acknowledgement
of the access probe is received from the service network, and the
another access probe is transmitted using the last increased
transmission power within the probe sequence; and the another
access probe is retransmitted using the last increased transmission
power in a predetermined number of repeats within the probe
sequence, and the controller module further increases the last
increased transmission power for the retransmissions of the another
access probe after the predetermined number of repeats within the
probe sequence, and uses the last increased transmission power
within the probe sequence for the retransmissions of the another
access probe within a next probe sequence.
7. A method for access procedure enhancement by a mobile
communication device comprising a wireless module capable of
wireless transmissions and receptions, comprising: transmitting an
access probe to a service network via the wireless module;
retransmitting the access probe in response to not receiving any
acknowledgement of the access probe from the service network via
the wireless module in a waiting period of time, wherein the
waiting period of time is determined according to a coherence-time
related offset; and repeating the retransmission of the access
probe until an acknowledgement of the access probe is received from
the service network via the wireless module.
8. The method of claim 7, wherein the access probe is first
transmitted using a transmission power which is determined
according to reverse-link load information of the service
network.
9. The method of claim 7, wherein the access probe is first
transmitted using a transmission power and retransmitted according
to one of the following: using the same transmission power in a
predetermined number of repeats within a probe sequence, and
increasing the transmission power for the retransmissions of the
access probe after the predetermined number of repeats within the
probe sequence; using the same transmission power within the probe
sequence, and increasing the transmission power for the
retransmissions of the access probe within a next probe sequence;
and using the transmission power with an incremental manner for the
retransmission of the access probe in each repeat within the probe
sequence.
10. The method of claim 7, wherein the service network broadcasts
reverse-link load information, and the method further comprises
determining a cell in the service network to which the access probe
is transmitted according to the reverse-link load information.
11. The method of claim 7, wherein the access probe comprises
information concerning a length of message data, and the method
further comprises transmitting another access probe with the
message data to the service network via the wireless module in
response to receiving a pre-acknowledgement of the access probe
from the service network via the wireless module.
12. The method of claim 11, wherein the access probe and the
another access probe are transmitted and retransmitted respectively
according to the following: the access probe is first transmitted
using a transmission power within a probe sequence, and the method
further comprises increasing the transmission power for the
retransmission of the access probe in each repeat within the probe
sequence until the pre-acknowledgement of the access probe is
received from the service network, and the another access probe is
transmitted using the last increased transmission power within the
probe sequence; and the another access probe is retransmitted using
the last increased transmission power in a predetermined number of
repeats within the probe sequence, and the method further comprises
increasing the last increased transmission power for the
retransmissions of the another access probe after the predetermined
number of repeats within the probe sequence, and using the last
increased transmission power within the probe sequence for the
retransmissions of the another access probe within a next probe
sequence.
13. A service network for access procedure enhancement, comprising:
a radio access network performing wireless transmissions and
receptions to and from a mobile communication device; and a control
node receiving an access probe from the mobile communication device
via the radio access network, determining whether the access probe
indicates that a length of message data is less than a threshold,
and transmitting a pre-acknowledgement of the access probe to the
mobile communication device via the radio access network in
response to the length of the message data being less than the
threshold.
14. The service network of claim 13, wherein the control node
further determines whether the access probe is decodable in
response to detecting a preamble in the access probe, broadcasts
another pre-acknowledgement with information of the access probe
via the radio access network in response to the access probe being
non-decodable, and after transmitting the pre-acknowledgement of
the access probe, receives another access probe with the message
data from the mobile communication device via the radio access
network and transmits an acknowledgement of the another access
probe to the mobile communication device via the radio access
network.
15. The service network of claim 13, wherein the control node
further broadcasts information concerning reverse-link load
information of the service network to the mobile communication
device via the radio access network.
16. A method for access procedure enhancement by a service network
comprising a radio access network, comprising: receiving an access
probe from a mobile communication device via the radio access
network; determining whether the access probe indicates that a
length of message data is less than a threshold; and transmitting a
pre-acknowledgement of the access probe to the mobile communication
device via the radio access network in response to the length of
the message data being less than the threshold.
17. The method of claim 16, further comprising: determining whether
the access probe is decodable in response to detecting a preamble
in the access probe; broadcasting another pre-acknowledgement with
information of the access probe via the radio access network in
response to the access probe being non-decodable; and after
transmitting the pre-acknowledgement of the access probe, receiving
another access probe with the message data from the mobile
communication device via the radio access network and transmitting
an acknowledgement of the another access probe to the mobile
communication device via the radio access network.
18. The method of claim 16, further comprising broadcasting
information concerning reverse-link load information of the service
network to the mobile communication device.
19. A mobile communication system for access procedure enhancement,
comprising: a mobile communication device transmitting an access
probe, retransmitting the access probe in response to not receiving
an acknowledgement of the access probe in a waiting period of time,
and repeating the retransmission of the access probe until the
acknowledgement of the access probe is received, wherein the
waiting period of time is determined according to a coherence-time
related offset; and a service network transmitting the
acknowledgement of the access probe to the mobile communication
device in response to receiving the access probe or the
retransmitted access probe.
20. The mobile communication system of claim 19, wherein the access
probe is first transmitted using a transmission power which is
determined according to reverse-link load information of the
service network.
21. The mobile communication system of claim 19, wherein the access
probe is first transmitted using a transmission power and
retransmitted according to one of the following: using the same
transmission power in a predetermined number of repeats within a
probe sequence, and the mobile communication device further
increases the transmission power for the retransmissions of the
access probe after the predetermined number of repeats within the
probe sequence; using the same transmission power within a probe
sequence, and the mobile communication device further increases the
transmission power for the retransmissions of the access probe
within a next probe sequence; and using the transmission power with
an incremental manner for the retransmission of the access probe in
each repeat within the probe sequence.
22. The mobile communication system of claim 19, wherein the
service network broadcasts reverse-link load information, and the
mobile communication device further determines a cell in the
service network to which the access probe is transmitted according
to the reverse-link load information.
23. The mobile communication system of claim 19, wherein the access
probe comprises information concerning a length of message data,
and the mobile communication device further transmits another
access probe with the message data to the service network via the
wireless module in response to receiving a pre-acknowledgement of
the access probe from the service network via the wireless
module.
24. The mobile communication system of claim 23, wherein the access
probe and the another access probe are transmitted and
retransmitted respectively according to the following: the access
probe is first transmitted using a transmission power within a
probe sequence, and the mobile communication device further
increases the transmission power for the retransmission of the
access probe in each repeat within the probe sequence until the
pre-acknowledgement of the access probe is received from the
service network, and the another access probe is transmitted using
the last increased transmission power within the probe sequence;
and the another access probe is retransmitted using the last
increased transmission power in a predetermined number of repeats
within the probe sequence, and the mobile communication device
further increases the last increased transmission power for the
retransmissions of the another access probe after the predetermined
number of repeats within the probe sequence, and uses the last
increased transmission power within the probe sequence for the
retransmissions of the another access probe within a next probe
sequence.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims the benefit of U.S. Provisional
Application No. 61/239,763, filed on Sep. 3, 2009, the entirety of
which is incorporated by reference herein, and this Application
also claims the benefit of U.S. Provisional Applications No.
61/241,003, filed on Sep. 9, 2009, the entirety of which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention generally relates to control signaling over
access channels in mobile communication systems, and more
particularly, to access procedure enhancements for mobile
communication systems.
[0004] 2. Description of the Related Art
[0005] For a long time, various machines have been provided to make
our lives more convenient in every way. Generally, machines,
nowadays, are equipped with computing processors and software to
accommodate us with more intelligence-based services. With the
advancement of wireless communications, Machine-to-Machine (M2M)
technology has been developed to enable communications between
remote machines for exchanging information and operating without
human interaction. Especially for critical public infrastructures,
such as water treatment facilities or bridges, M2M sensors may be
employed to monitor the operation statuses of facilities and report
measurement results back to control centers via wireless
communication networks, such as Global System for Mobile
Communication/General Packet Radio Service (GSM/GPRS), Universal
Mobile Telecommunication System (UMTS), 1x Code Division Multiple
Access 2000 (1x CDMA 2000) system, 1x High Rate Packet Data
(1xHRPD) system, and Long Term Evolution (LTE) system, etc. This
would allow administrators of the critical public infrastructures
to know if certain elements have been tampered with. Other
applications may be electric meters, gas line monitoring devices,
or coke machines that report their operation statuses to a
centralized system via wireless communication networks, to provide
related services with higher efficiency and lower maintenance
costs.
[0006] It is noted that the amount of data per report is usually
small, so preferably, an access channel is used by most M2M
machines to transmit the data traffic. FIG. 1 is a block diagram
illustrating a conventional access procedure of an M2M machine. To
begin, the M2M machine first performs a persistence check to see if
another M2M machine is transmitting data on the access channel. If
not, it transmits an access probe with an initial transmission
power. Subsequently, the M2M machine waits for a response of the
access probe for a period of time (denoted as T.sub.p). If no
response of the access probe is received during T.sub.p, the M2M
machine increases the transmission power and uses the increased
transmission power to retransmit the access probe. During each
probe sequence, the retransmission of the access probe is repeated
using incremental transmission power until a response of the access
probe is received or a maximum number of retries (denoted as
N.sub.p) is reached. If no response of the access probe is received
during a probe sequence of retransmission, the M2M machine further
holds for another period of time (denoted as T.sub.s) and then
initiates another probe sequence of retransmission. However, it is
noted that the access channel is a shared common channel for all
M2M machines in the same service area and too many retransmissions
of the access probe may cause unnecessary occupancy over the access
channel. That is, collision of access probes transmitted by
different M2M machines may occur frequently and result in
throughput degression for the entire M2M system.
[0007] In addition, when selecting an access network (referred to
as AN herein) to initiate the access procedure, the conventional
M2M machine only takes into account the pilot strength of the
detected ANs, and transmits the access probe to the AN with the
highest pilot strength. However, if the reverse-link (referred to
as RL herein) load of the selected AN is heavy, the interference on
the RL will be great. In this case, the delivery of the access
probe is not only likely to fail, but also introduces more
interference on the RL. Thus, it is desirable to have a novel
access procedure in which the radio resources of the access channel
may be efficiently utilized to improve the overall system
throughput.
BRIEF SUMMARY OF THE INVENTION
[0008] Accordingly, embodiments of the invention provide
apparatuses, systems, and methods for access procedure enhancement.
In one aspect of the invention, a mobile communication device for
access procedure enhancement is provided. The mobile communication
device comprises a wireless module and a controller module. The
wireless module performs wireless transmissions and receptions to
and from a service network. The controller module transmits an
access probe to the service network via the wireless module, and
retransmits the access probe in response to not receiving an
acknowledgement of the access probe from the service network via
the wireless module in a waiting period of time. Also, the
controller module further repeats the retransmission of the access
probe until the acknowledgement of the access probe is received
from the service network via the wireless module, wherein the
waiting period of time is determined according to a coherence-time
related offset.
[0009] In another aspect of the invention, a method for access
procedure enhancement by a mobile communication device comprising a
wireless module capable of wireless transmissions and receptions is
provided. The method comprises the steps of transmitting an access
probe to a service network via the wireless module, retransmitting
the access probe in response to not receiving any acknowledgement
of the access probe from the service network via the wireless
module in a waiting period of time, wherein the waiting period of
time is determined according to a coherence-time related offset,
and repeating the retransmission of the access probe until an
acknowledgement of the access probe is received from the service
network via the wireless module.
[0010] In another aspect of the invention, a service network for
access procedure enhancement is provided. The service network
comprises a radio access network and a control node. The radio
access network performs wireless transmissions and receptions to
and from a mobile communication device. The control node receives
an access probe from the mobile communication device via the radio
access network, and determines whether the access probe indicates
that a length of message data is less than a threshold. Also, the
control node transmits a pre-acknowledgement of the access probe to
the mobile communication device via the radio access network in
response to the length of the message data being less than the
threshold.
[0011] In another aspect of the invention, a mobile communication
system for access procedure enhancement is provided. The mobile
communication system comprises a mobile communication device and a
service network. The mobile communication device transmits an
access probe, retransmits the access probe in response to not
receiving an acknowledgement of the access probe in a waiting
period of time, and repeats the retransmission of the access probe
until the acknowledgement of the access probe is received, wherein
the waiting period of time is determined according to a
coherence-time related offset. The service network transmits the
acknowledgement of the access probe to the mobile communication
device in response to receiving the access probe or the
retransmitted access probe.
[0012] Other aspects and features of the invention will become
apparent to those with ordinary skill in the art upon review of the
following descriptions of specific embodiments of the mobile
communication device, the service network, the mobile communication
system, and the method for access procedure enhancement.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0014] FIG. 1 is a block diagram illustrating a conventional access
procedure of an M2M machine;
[0015] FIG. 2 is a block diagram illustrating a mobile
communication system according to an embodiment of the
invention;
[0016] FIG. 3 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to an embodiment of the invention;
[0017] FIG. 4 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to another embodiment of the invention;
[0018] FIG. 5 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to yet another embodiment of the invention;
[0019] FIG. 6 is a flow chart illustrating the method for access
procedure enhancement according to an embodiment of the
invention;
[0020] FIG. 7 is a schematic diagram illustrating the structures of
the access probe before and after receiving a pre-acknowledgement
according to an embodiment of the invention;
[0021] FIG. 8 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to the embodiment of FIG. 7;
[0022] FIG. 9 is a schematic diagram illustrating the structures of
the access probe before and after receiving a pre-acknowledgement
according to another embodiment of the invention;
[0023] FIG. 10 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to the embodiment of FIG. 9; and
[0024] FIG. 11 is another schematic diagram illustrating the
detailed operation of the mobile communication device 210 during an
access procedure according to the embodiment of FIG. 9.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
[0026] FIG. 2 is a block diagram illustrating a mobile
communication system according to an embodiment of the invention.
In the mobile communication system 200, the mobile communication
device 210 is wirelessly connected to the service network 220 via
an air interface, and performs wireless transmissions and
receptions to and from the service network 220. The mobile
communication device 210 comprises a wireless module 211 for
performing the functionality of wireless transmissions and
receptions. To further clarify, the wireless module 211 may
comprise a baseband unit (not shown) and a radio frequency (RF)
unit (not shown). The baseband unit may contain multiple hardware
devices to perform baseband signal processing, including analog to
digital conversion (ADC)/digital to analog conversion (DAC), gain
adjusting, modulation/demodulation, encoding/decoding, and so on.
The RF unit may receive RF wireless signals, convert the received
RF wireless signals to baseband signals, which are processed by the
baseband unit, or receive baseband signals from the baseband unit
and convert the received baseband signals to RF wireless signals,
which are later transmitted. The RF unit may also contain multiple
hardware devices to perform radio frequency conversion. For
example, the RF unit may comprise a mixer to multiply the baseband
signals with a carrier oscillated in the radio frequency of the
wireless communications system, wherein the radio frequency may be
900 MHz, 1800 MHz or 1900 MHz utilized in GSM systems, or may be
900 MHz, 1900 MHz or 2100 MHz utilized in WCDMA systems, or others
depending on the radio access technology (RAT) in use. Also, the
mobile communication device 210 comprises a controller module 212
for controlling the operation of the wireless module 211 and other
function components, such as a display unit and/or keypad serving
as the MMI (man-machine interface), a storage unit storing the
program codes of applications or communication protocols, or
others. To be more specific, the controller module 212 controls the
wireless module 311 to perform an access procedure with the service
network 220. The controller module 212 first transmits an access
probe to the service network 220 via the wireless module 211, and
then awaits an acknowledgement of the access probe from the service
network 220 for a waiting period of time. Note that the waiting
period of time is determined according to a coherence-time related
offset. If no acknowledgement of the access probe is received from
the service network 220 via the wireless module 211 in the waiting
period of time, the controller module 212 retransmits the access
probe to the service network 220 via the wireless module 211.
Basically, the controller module 212 repeats the retransmission of
the access probe until the acknowledgement of the access probe is
received from the service network 220 via the wireless module 211.
In addition to the wireless module 211 and the controller module
212, the mobile communication device 210 may contain other
components, such as sensors for detecting temperature, pressure,
vibration, and/or water line, according to the appliance of the
mobile communication device 210. For example, the mobile
communication device 210 may be a monitoring device coupled to/in a
waterworks facility, bridge, electric meter, gas line device, coke
machine, or others.
[0027] FIG. 3 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to an embodiment of the invention. Unlike the
conventional design as described above, the waiting period of time
between the transmissions/retransmissions of access probes
(referred to as T.sub.p' herein) is extended in the access
procedure to avoid access probe collisions since the traffic of M2M
communications is usually delay insensitive. Specifically, the
extension of the waiting period of time is determined by taking
into account the coherence time for wireless transmissions between
the mobile communication device 210 and the service network 220. In
one embodiment, T.sub.p' may be derived from equation (1) as
follows:
T.sub.p'=T.sub.ACMPATProbeTimeout+(y.sub.Total.times.AccessCycleDuration-
)-ProbeTimeOutAdjst+M2MOffset (1)
wherein T.sub.ACMPATProbeTimeout is the time for receiving the
acknowledgement of the access probe, y.sub.Total is a uniformly
distributed integer random number, AccessCycleDuration is the
duration of an Access channel Cycle in units of slots, which
specifies the time instants at which the access terminal may start
transmitting/retransmitting an access probe, and ProbeTimeOutAdjust
is the parameter to set the time-out adjustment of each access
probe. Most importantly, in the equation (1), an additional time
offset for M2M communications, i.e. M2MOffset, is introduced for
the purpose of extending the waiting period of time. The value of
M2MOffset may be configured in the range from 0 to 6.828 seconds,
where the value is negotiable between the mobile communication
device 210 and the service network 220 for ensuring that T.sub.p'
is larger than the coherence time for wireless transmissions
between the mobile communication device 210 and the service network
220. For example, the coherence time may be 0.667 seconds (derived
from the Doppler Frequency Shift specified in the specification
3GPP2 C.R1002) for static M2M devices, and M2MOffset may be
configured to a certain value so that T.sub.p' is larger than 0.667
seconds. In addition to the extension of the waiting period of
time, the transmission power used to transmit/retransmit the access
probe is further controlled in a way that the same transmission
power is used for the first 2 transmission/retransmission of the
access probe and then the transmission power is scaled up to a
certain level for the next 2 retransmissions of the access probe in
the same probe sequence, as shown in FIG. 3. The increment of the
transmission power used is repeated until an acknowledgement of the
access probe is received from the service network 220 or a maximum
number of retries is reached. It is to be understood that 2 times
of the same transmission power applied is just an example, and
other number of times of the same transmission power applied may be
contemplated for those skilled in the art. Note that, in the second
probe sequence, a new waiting period of time is calculated by the
equation (1) and the transmission power is reset to the initial
level in the first probe sequence. With the extension of the
waiting period of time, not only are collisions of access probes
avoided, but also the mobile communication device 210 may get more
time to measure the pilot strength. By averaging the long-measured
pilot strength, a more accurate estimation of the pilot strength
and received power may be obtained, so that the mobile
communication device 210 may determine a more appropriate
transmission power. In addition, the instant fast fading on the
wireless links may be eliminated due to the extension of the
waiting period of time.
[0028] FIG. 4 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to another embodiment of the invention. Similar
to FIG. 3, the waiting period of time between the
transmissions/retransmissions of access probes is extended in the
access procedure by adding an additional time offset as described
above with the equation (1). However, as shown in FIG. 4, the
transmission powers used for all transmission and retransmissions
of the access probe in each probe sequence is set to the same
level. Specifically, the transmission power used in the first probe
sequence is set to an initial level, and the transmission power
used in the second probe sequence is scaled up from to a certain
level larger than the initial level, and so on. It is noted that
the mobile communication device 210 further employs the open-loop
power control for determining the initial transmission power used
in each probe sequence.
[0029] FIG. 5 is a schematic diagram illustrating the detailed
operation of the mobile communication device 210 during an access
procedure according to yet another embodiment of the invention.
Similar to FIGS. 3 and 4, the waiting period of time between the
transmissions/retransmissions of access probes is extended in the
access procedure by adding an additional time offset as described
above with the equation (1). However, as shown in FIG. 5, the
transmission power used is scaled up for every retransmission in
each probe sequence. Specifically, in the first probe sequence, the
waiting period of time is calculated by the equation (1) and the
transmission power of the access probe is selected in an
incremental manner, and in the second probe sequence, the waiting
period of time is re-calculated by the equation (1) and the
transmission power of the access probe is selected in the same
incremental manner, and so on until an acknowledgement of the
access probe is received or a maximum number of retries is reached.
The maximum number of retries is a configurable parameter. In one
embodiment, the maximum number of retries is determined by the
broadcasted system information from the service network 220.
[0030] FIG. 6 is a flow chart illustrating the method for access
procedure enhancement according to an embodiment of the invention.
In this embodiment, the method is applied to the mobile
communication device 210. To begin, the mobile communication device
210 transmits an access probe to the service network 220 via the
wireless module 211 (step S610). In response to not receiving any
acknowledgement of the access probe from the service network 220
via the wireless module 211 in a waiting period of time, e.g.
T.sub.p', the mobile communication device 210 retransmits the
access probe to the service network 220 via the wireless module
211, wherein the waiting period of time is determined according to
a coherence-time related offset (step S620). In one embodiment, the
coherence-time related offset may be the parameter M2MOffset, as
described in FIG. 3, considering the coherence time for wireless
transmissions between the mobile communication device 210 and the
service network 220. Subsequently, the mobile communication device
210 repeats the retransmission of the access probe until an
acknowledgement of the access probe is received from the service
network 220 via the wireless module 211 (step S630). Note that the
waiting period of time is extended when compared with the
conventional access procedure to avoid access probe collisions. In
addition to the extension of the waiting period of time, the method
further adjusts the transmission power for the retransmissions of
the access probe. In one embodiment, the access probe may be first
transmitted using a transmission power and then the same
transmission power is used for a predetermined number of
retransmissions within a probe sequence. Taking the example shown
in FIG. 3, the predetermined number of retransmissions is set to 1.
Later, if the acknowledgement of the access probe is not yet
received from the service network 220, the method may further
enable the mobile communication device 210 to increase the
transmission power for the next 2 retransmissions of the access
probe within the same probe sequence. The increment of the
transmission power may be performed repeatedly until the
acknowledgement of the access probe is not yet received. In another
embodiment, the method may enable the mobile communication device
210 to use the same transmission power of the first transmission
for all the retransmissions within a probe sequence and increase
the transmission power for the retransmissions within a next probe
sequence, as described with respect to FIG. 4. Alternatively, in
yet another embodiment, the method may enable the mobile
communication device 210 to increase the transmission power for
each transmission/retransmission of the access probe within a probe
sequence, as described with respect to FIG. 5. Note that the mobile
communication device 210 is operating in non-slotted mode where
continuous monitoring of the paging channel is required, and the
wireless technology used for the communications between the mobile
communication device 210 and the service network 220 is 1xHRPD Rev.
C, while other wireless technologies, such as the GSM/GPRS, UMTS,
1xCDMA 2000, and LTE, may be employed as well without departing
from the spirit of the invention.
[0031] In order to enhance the throughput of M2M communications,
when selecting a target AN (assuming that the service network 210
further comprises a plurality of ANs) to initiate an access
procedure, the mobile communication device 210 takes into account
not only the pilot strength of the ANs but also the RL load
information of the ANs. In one embodiment, the ANs in the service
network 220 may each broadcast its RL load information to the
mobile communication device 210. The RL load information may
comprise an RL load level, referred to as .mu..sub.(p,t), for each
neighboring AN's pilot p for all carriers at time t, a minimum
server quality .gamma. or a minimum transmission power headroom,
and an RL open-loop adjust value for open-loop power control. Based
on the RL load information, the mobile communication device 210 may
first select the ANs having the highest value of
SINR.sub.(p,t)-.mu..sub.(p,t). Subsequently, the mobile
communication device 210 selects one target AN with the lightest RL
load to initiate the access procedure. In this way, the access
procedure may be performed in a fair-quality AN with light RL load,
so M2M communications between the mobile communication device 210
and the service network 220 will be smooth.
[0032] It is noted that the open-loop power control employed for
determining the initial transmission of the access probe in each
probe sequence is further enhanced by the mobile communication
device 210. Specifically, the mobile communication device 210
determines the initial transmission of the access probe in each
probe sequence according to the RL load status of the target AN.
The RL load status of the target AN may be obtained from the
broadcasted system information from the target AN, or from the
Reverse Activity Bit (RAB) indicated in MAC index 4. The Reverse
Activity Bit is transmitted to indicate the load status on reverse
link. Based on this information, the terminal can change its data
rate on the reverse link. The mobile communication device 210 first
determines an additional adjustment factor, denoted as LoadAdjust,
according to the RL load status of the target AN, and then
determines the mean output power for the open-loop power control
with the equation as follows:
Initial_TxPower=-MeanRxPower+OpenLoopAdjust+ProbeInitialAdjust+LoadAdjus-
t (2)
wherein MeanRxPower is the mean estimation of received power,
OpenLoopAdjust is the nominal power to be used by the access
terminal in open loop power control, and ProbeInitialAdjust is a
correction factor to be used by the access terminal in open loop
power control. Both OpenLoopAdjust and ProbeInitialAdjust are
specified in an AccessParameters message. Note that the adjustment
factor, LoadAdjust, may be calculated by the mobile communication
device 210 according to the broadcasted system information or the
RAB, or the mobile communication device 210 may maintain a mapping
table describing the mapping relationship between the RL load
status and the adjustment factor, LoadAdjust. Alternatively, the
ANs in the service network 220 may include the adjustment factor,
LoadAdjust, together with the RL load status in the broadcasted
system information.
[0033] In addition, a pre-acknowledgement mechanism is provided to
improve the reduction in interference on the access channel. That
is, by transmitting a pre-acknowledgement of the received access
probe, the service network 220 may indicate to the mobile
communication device 210 that the service network 220 has detected
the preamble or decoded the header part of the received access
probe. Thus, a different structure of the access probe may be
employed by the mobile communication device 210. FIG. 7 is a
schematic diagram illustrating the structures of the access probe
before and after receiving a pre-acknowledgement according to an
embodiment of the invention. Before receiving a pre-acknowledgement
from the service network 220, the mobile communication device 210
may only include the preamble, the message header, and the message
length in the access probe (denoted with a white bar as shown in
the upper half of FIG. 7) without the message data. This would
shorten the duration of access probe and reduce possible
interference on the access channel. When receiving the access
probe, the service network 320 may determine whether to transmit a
pre-acknowledgement or set up a traffic channel for the mobile
communication device 210 according to the message length. For
example, if the message length indicates that a large amount of
data is to be transmitted, the service network 220 may determine to
set up a traffic channel for the mobile communication device 210
since the access channel is more appropriate for transmitting small
amounts of data. Otherwise, if the message length indicates that a
small amount of data is to be transmitted, the service network 220
may determine to transmit a pre-acknowledgement to the mobile
communication device 210. After receiving the pre-acknowledgement
from the service network 220, the mobile communication device 210
may instead include the preamble, the message header, and the
message data in the access probe (denoted with a gray bar as shown
in the lower half of FIG. 7). Since receiving the
pre-acknowledgement may imply that the service network 220 is able
to detect the preamble or decode the message header in the access
probe, the transmission power used for the access probe may be
enough for the delivery of the access probe. Thus, the transmission
power used for the pre-acked access probe may be used for all the
subsequent retransmissions of the access probe, as shown in FIG.
8.
[0034] FIG. 9 is a schematic diagram illustrating the structures of
the access probe before and after receiving a pre-acknowledgement
according to another embodiment of the invention. Before receiving
a pre-acknowledgement from the service network 220, the mobile
communication device 210 may only include the preamble and the
message header in the access probe (denoted with a white bar as
shown in the upper half of FIG. 10) without the message data,
wherein the message header further comprises the message length.
When receiving the access probe, the service network 320 may
determine whether to transmit a pre-acknowledgement or set up a
traffic channel for the mobile communication device 210 according
to the message length, as described above. After receiving the
pre-acknowledgement from the service network 220, the mobile
communication device 210 may instead include the preamble, the
message header, and the message data in the access probe (denoted
with a gray bar as shown in the lower half of FIG. 10), wherein the
message header may or may not comprise the message length. Since
receiving the pre-acknowledgement may imply that the service
network 220 is able to detect the preamble or decode the message
header in the access probe, the transmission power used for the
access probe may be enough for the delivery of the access probe.
Thus, the transmission power used for the pre-acked access probe
may be used for all the subsequent retransmissions of the access
probe, as shown in FIG. 10. Alternatively, the transmission power
used for the pre-acked access probe may be used for only a
predetermined number of the subsequent retransmissions, and after
that, the transmission power may be scaled up for the next
predetermined number of the subsequent retransmissions, as shown in
FIG. 11, until an acknowledgement of the access probe is received
from the service network 220 or the maximum number of retries is
reached. Note that the initial transmission power for the
retransmissions in the probe sequence after the pre-acknowledgement
is received may be set to the same transmission power used for the
pre-acked access probe.
[0035] In yet another embodiment, the mobile communication device
210 may always include the entire message packet in the access
probe. When detecting the preamble of the access probe, the service
network 220 may broadcast a pre-acknowledgement to all mobile
communication devices to indicate that a non-decodable access probe
has been received, so that other mobile communication devices may
change their access timing of the next access probes to avoid
collisions and reduce interference on the access channel.
[0036] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. Those who are skilled in this
technology can still make various alterations and modifications
without departing from the scope and spirit of this invention. For
example, the wireless technology employed by the mobile
communication device 210 and the service network 220 may be the
GSM/GPRS, UMTS, 1xCDMA 2000, or LTE technology. Therefore, the
scope of the invention shall be defined and protected by the
following claims and their equivalents.
* * * * *